Radio Monitoring and High-Resolution Imaging of extreme Blazars and other TeV-Detected Active Galaxies with the Effelsberg 100-m Telescope and the Global Millimetre VLBI Array

• Applicant: Professor Dr. Matthias Kadler
• Subject Area: Astrophysics and Astronomy
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 465409577

Extreme blazars represent a sub-class of active galaxies with collimated relativistic plasma jets, whose emission maxima range to higher energies by several orders of magnitude as compared to 'regular' blazars, reaching far into the TeV gamma-ray regime. Although only a small number of extreme blazars is known today, it is clear that they represent a numerous class of objects of high relevance for the upcoming decade of research in high-energy astronomy and astropartiale physics. Extreme blazars are of particular interest in the context of the still not understood sources of ultrahigh-energy cosmic rays and their associated processes of extreme particle acceleration, as well as possible sources of high-energy astrophysical neutrinos. The radio regime offers unprecedented possibilities of high angular-resolution imaging and high-sensitivity spectral flux-density studies to probe the structure and dynamical processes in such relativistic plasma jets. The radio emission of extreme blazars is comparatively faint and not yet well studied. In this project, we will combine a new long-term spectral monitoring program of TeV-blazars using the Effelsberg 100-m radio telescope with a radio-interferometric high-resolution imaging study of a sample of extreme blazars with the global Millimeter VLBI Array (GMVA). The Effelsberg program will characterize the radio variability properties of TeV blazars and their faint polarized emission, providing data to determine their dynamic broadband emission from the radio to the TeV-gamma regime. This will allow us to constrain the site of origin of the TeV gamma-ray emission. The GMVA observations will provide sub-parsec-scale details on characteristic structures such as jet limb brightening, predicted by gamma-ray emission models, and will yield a systematic study of brightness temperatures, core spectra and jet velocities on the most compact scales of the jets that are accessible via mm-VLBI, ultimately comparing extreme blazars with other classes of TeV-emitting blazars.

• DFG Programme: Research Grants
• Co-Investigators: Dr. Alexander Kraus; Professor Dr. Eduardo Ros